I have never tried Eton Mess. However, meringue, double cream, fruit, mozzarella and chocolate over a very thin pizza base sounds like something a four year old would do if you gave him run of the kitchen. Mixing that much fat and sugar strikes me as nauseating.
I've never tried anything like that for the same reason I would never eat chocolate mixed with peanut butter, hamburger and marsipan, despite these all being things that I enjoy eating.